IPv4 Addressing:
IPv4 addresses are 32-bit binary numbers divided into 4 octets, represented in dotted decimal notation.
Private IP addresses are reserved for use within a private network and are not routed on the internet.
Public IP addresses are used for communication on the internet and are unique.
Subnetting:
Subnetting allows a single network to be divided into smaller sub-networks or subnets.
Subnetting is performed by borrowing bits from the host portion of the IP address.
The number of subnets created is determined by the number of bits borrowed.
The number of hosts per subnet is determined by the number of remaining host bits.
Classful Subnetting:
Classful subnetting divides the address into three portions: network, subnet, and host.
Class A, B, and C address ranges determine the number of bits available for subnetting and the maximum number of hosts per subnet.
CIDR (Classless Inter-Domain Routing):
CIDR replaces classful subnetting and allows for more efficient use of IP addresses.
CIDR uses a prefix length to specify the number of bits in the network portion of an IP address.
CIDR notation is represented as a dotted decimal IP address followed by a forward slash and the prefix length.
Subnet Mask:
A subnet mask is used to divide the IP address into the network and host portions.
The subnet mask is a 32-bit binary number, typically represented in dotted decimal notation.
The subnet mask is used to determine the network address and broadcast address of a subnet.
VLSM (Variable Length Subnet Masks):
VLSM allows for creation of subnets of different sizes within a single network.
VLSM allows for more efficient use of IP addresses by allocating only the required number of host addresses to each subnet.
IPv4 Address Summary:
IPv4 addresses are 32-bit binary numbers divided into 4 octets.
IPv4 addresses can be either private or public.
Subnetting divides a network into smaller sub-networks.
Classful subnetting divides the IP address into network, subnet, and host portions.
CIDR replaces classful subnetting and allows for more efficient use of IP addresses.
A subnet mask is used to divide the IP address into the network and host portions.
VLSM allows for creation of subnets of different sizes within a single network.
Class address ranges:
- Class A = 1.0.0.0 to 126.0.0.0
- Class B = 128.0.0.0 to 191.255.0.0
- Class C = 192.0.1.0 to 223.255.255.0
Reserved address ranges for private (non-routed) use:
- 10.0.0.0 -> 10.255.255.255
- 172.16.0.0 -> 172.31.255.255
- 192.168.0.0 -> 192.168.255.255
Other reserved addresses:
- 127.0.0.0 is reserved for loopback and IPC on the local host
- 224.0.0.0 -> 239.255.255.255 is reserved for multicast addresses
Chart notes:
- Number of Subnets - "( )" Refers to the number of effective subnets, since the use of subnet numbers of all 0s or all 1s is highly frowned upon and RFC non-compliant.
- Number of Hosts - Refers to the number of effective hosts, excluding the network and broadcast address.
Class A
| Network Bits | Subnet Mask | Number of Subnets | Number of Hosts |
| /8 | 255.0.0.0 | 0 | 16777214 |
| /9 | 255.128.0.0 | 2 (0) | 8388606 |
| /10 | 255.192.0.0 | 4 (2) | 4194302 |
| /11 | 255.224.0.0 | 8 (6) | 2097150 |
| /12 | 255.240.0.0 | 16 (14) | 1048574 |
| /13 | 255.248.0.0 | 32 (30) | 524286 |
| /14 | 255.252.0.0 | 64 (62) | 262142 |
| /15 | 255.254.0.0 | 128 (126) | 131070 |
| /16 | 255.255.0.0 | 256 (254) | 65534 |
| /17 | 255.255.128.0 | 512 (510) | 32766 |
| /18 | 255.255.192.0 | 1024 (1022) | 16382 |
| /19 | 255.255.224.0 | 2048 (2046) | 8190 |
| /20 | 255.255.240.0 | 4096 (4094) | 4094 |
| /21 | 255.255.248.0 | 8192 (8190) | 2046 |
| /22 | 255.255.252.0 | 16384 (16382) | 1022 |
| /23 | 255.255.254.0 | 32768 (32766) | 510 |
| /24 | 255.255.255.0 | 65536 (65534) | 254 |
| /25 | 255.255.255.128 | 131072 (131070) | 126 |
| /26 | 255.255.255.192 | 262144 (262142) | 62 |
| /27 | 255.255.255.224 | 524288 (524286) | 30 |
| /28 | 255.255.255.240 | 1048576 (1048574) | 14 |
| /29 | 255.255.255.248 | 2097152 (2097150) | 6 |
| /30 | 255.255.255.252 | 4194304 (4194302) | 2 |
Class B
| Network Bits | Subnet Mask | Number of Subnets | Number of Hosts |
| /16 | 255.255.0.0 | 0 | 65534 |
| /17 | 255.255.128.0 | 2 (0) | 32766 |
| /18 | 255.255.192.0 | 4 (2) | 16382 |
| /19 | 255.255.224.0 | 8 (6) | 8190 |
| /20 | 255.255.240.0 | 16 (14) | 4094 |
| /21 | 255.255.248.0 | 32 (30) | 2046 |
| /22 | 255.255.252.0 | 64 (62) | 1022 |
| /23 | 255.255.254.0 | 128 (126) | 510 |
| /24 | 255.255.255.0 | 256 (254) | 254 |
| /25 | 255.255.255.128 | 512 (510) | 126 |
| /26 | 255.255.255.192 | 1024 (1022) | 62 |
| /27 | 255.255.255.224 | 2048 (2046) | 30 |
| /28 | 255.255.255.240 | 4096 (4094) | 14 |
| /29 | 255.255.255.248 | 8192 (8190) | 6 |
| /30 | 255.255.255.252 | 16384 (16382) | 2 |
Class C
| Network Bits | Subnet Mask | Number of Subnets | Number of Hosts |
| /24 | 255.255.255.0 | 0 | 254 |
| /25 | 255.255.255.128 | 2 (0) | 126 |
| /26 | 255.255.255.192 | 4 (2) | 62 |
| /27 | 255.255.255.224 | 8 (6) | 30 |
| /28 | 255.255.255.240 | 16 (14) | 14 |
| /29 | 255.255.255.248 | 32 (30) | 6 |
| /30 | 255.255.255.252 | 64 (62) | 2 |
Class D
| CIDR Block | Supernet Mask | Number of Class C Addresses | Number of Hosts |
| /14 | 255.252.0.0 | 1024 | 262144 |
| /15 | 255.254.0.0 | 512 | 131072 |
| /16 | 255.255.0.0 | 256 | 65536 |
| /17 | 255.255.128.0 | 128 | 32768 |
| /18 | 255.255.192.0 | 64 | 16384 |
| /19 | 255.255.224.0 | 32 | 8192 |
| /20 | 255.255.240.0 | 16 | 4096 |
| /21 | 255.255.248.0 | 8 | 2048 |
| /22 | 255.255.252.0 | 4 | 1024 |
| /23 | 255.255.254.0 | 2 | 512 |
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